Biological Control of Insect Pests on Field Crops in Kansas

Biological Control of Insect Pests on Field Crops in Kansas J.P. Michaud, P.E. Sloderbeck, and J.R. Nechols Biological Control beneficial practices can be integrated into production In the simplest terms, biological control is the systems in a cost-effective and convenient manner. This reduction of pest populations brought about through requires not only a good understanding of the biology the actions of other living organisms, often collectively and ecology of natural enemies, but also a willingness to referred to as natural enemies or beneficial species. modify production practices to accommodate their needs. Virtually all insect and mite pests have some natural Complicating matters is the fact that many beneficial enemies, although not all are effective in suppressing pest insects feed not only on pest insects, but also on each populations. Learning to recognize, manage, and conserve other, a phenomenon referred to as intraguild predation. natural enemies can help reduce pest populations and In a healthy agroecosystem with a high degree of plant maintain them below economic levels, thus reducing crop and insect diversity, naturally-occurring biological control losses and the need for more costly control measures that can go almost unnoticed because natural enemies are may also have undesirable environmental side-effects. effectively maintaining a plethora of potential pests at low Biological control is often most effective when densities. coupled with other pest control tactics in an integrated The most obvious harmful practice is the use of pest management (IPM) program. Practices that are insecticides at times when natural enemies are active. often compatible with biological control include cultural Insecticides have a wide range of adverse effects on controls, crop rotation, planting pest-resistant varieties, natural enemies, killing them directly, impairing their using insecticides with selective modes of action, or spot foraging and reproductive abilities, and depriving them of treatments that leave untreated areas to serve as refuges food. Nevertheless, there are various ways that insecticides for natural enemies. can be successfully integrated into a production system Effective biological control often requires a good while minimizing their impact on beneficial species. understanding of the biology of the pest and its natural Materials such as certain varieties of Bacillus enemies, as well as the ability to identify various life thuringensis (Bt) are selectively toxic to particular groups stages of relevant insects in the field. Field scouting of pest insects such as caterpillars and leave natural usually is necessary to monitor natural enemy activity, enemies unharmed. Unfortunately, most Bt formulations evaluate impact on pest populations, and anticipate the currently available lack good residual efficacy under need for additional control measures. Although three field conditions. The in-plant expression of Bt toxin in distinct approaches to biological control are recognized genetically-engineered corn and cotton varieties has (conservation, importation, and augmentation), the revolutionized the management of moth pests on these principles of conservation biological control are by far the crops and has so far proven compatible with biological most important for producers of field crops in Kansas to control of other pests, primarily through reduced understand. applications of hard insecticides. Conservation of Natural Enemies Several recently developed biorational materials such as spinosad and indoxacarb achieve selectivity through Natural enemy conservation is at once the most low contact toxicity; they must be consumed by the straightforward concept of biological control in the insect to be activated. Since natural enemies typically context of field crops, and the most complex. At the don’t eat plant material with the chemical on it, they are simplest level, conservation biological control means spared direct mortality. However, even materials with avoiding cultural practices that harm natural enemies high contact toxicity can be applied in ways that minimize and implementing practices that attract, encourage, or their impact on beneficial species. Insecticides with good benefit them. Although this may seem like common plant systemic activity (e.g., clothianidin, imidacloprid, sense, the challenging part is understanding exactly thiamethoxam) can be used as seed treatments, in-furrow, what practices are harmful to natural enemies and how 1 or as soil drench applications to be taken up by the harvesting practice provides a continuous refuge and food plants while causing little direct mortality to natural supply for beneficial insects. enemies. Finally, damaging pest populations are often Importation of Natural Enemies confined to portions of a field, rather than being evenly Today’s high volumes of international trade and distributed throughout it. Selective spot-treatment of airline traffic have increased the frequency of arrival affected areas will not only reduce application costs, it of exotic pests from other regions of the world. When will leave untreated areas to serve as reservoirs for natural immigrant pests succeed in establishing in a new enemies. These survivors can then recolonize treated areas geographic location they can rapidly reach very high following degradation of the insecticide, accelerating populations and cause serious economic losses, largely the restoration of biological control and sometimes because they lack the complex of natural enemies that averting the need for subsequent treatments. Nevertheless, limits their population growth in their country of origin. situations arise where the preservation of biological Examples of serious pests in Kansas of foreign origin control requires avoiding the broadcast application of any include the Hessian fly, the European corn borer, the insecticide. When biological control is widely disrupted Russian wheat aphid, and the alfalfa weevil. The selective by insecticide applications, minor pests can become major importation and release of natural enemies from the pest’s pests (secondary pest resurgence), and a farm can develop country of origin is also known as classical biological dependency on chemical control measures once natural control. This approach gained impetus early in the last enemies are no longer resident in the fields (the pesticide century following several dramatic successes, notably treadmill effect). the importation of the vedalia beetle to control cottony Certain cultural practices also can be detrimental cushion scale in California. However, only a small to natural enemies. Plowing, cultivation, mowing, or proportion of importations have met with this level of harvesting operations can be disruptive to natural enemies success and the general applicability of this approach to if they coincide with critical stages of their life cycle. all new invasive pests is currently a subject of considerable While the adoption of no-till and minimum tillage debate. Although large populations are often observed agriculture has favored the resurgence of some pests such when an exotic pest first invades, these often decline as false wireworms that utilize crop residues for food or over a period of years as the native community of natural harborage, such practices also favor various beneficial enemies gradually evolves to exploit them. Evidence is insects such as ground beetles, spiders, and other growing that many invasive pests ultimately come under generalist predators that rely on crop residues for cover, adequate biological control solely through the action which encourages their persistence in the field. Dust of native beneficial species. However, there are other raised by traffic along dirt roads or cultivation operations examples where native natural enemies do not — or carried out during dry weather can impede the foraging cannot — provide required levels of biological control. activities of beneficial insects when it is deposited in Classical biological control involves exploring a sufficient amounts on leaf surfaces. The burning of crop pest’s country of origin for a potentially effective natural residues can also kill large numbers of beneficial insects, as enemy, importing it to the pest’s adopted country, can inappropriately timed flood irrigation. Other practices and mass-rearing it in the laboratory for subsequent such as excessive herbicide applications on pastures and release in regions where the pest is active. The goal is fallow fields reduce both plant and insect diversity in non- to ultimately establish a self-sustaining population of crop habitats that normally serve as important reservoirs the natural enemy that maintains the pest population of many natural enemy species. These beneficial species below economic threshold levels for perpetuity. In this are then no longer available to colonize annual crops in regard, classical biological control differs from other adjacent fields as pest populations develop. forms of biological control in that it is not carried out One of the biggest hurdles for sustainable biological by the farmer or gardener, but only by scientists with control in field crops is the loss of plant and insect appropriate authorization from federal agencies, in diversity associated with large scale monoculture, particular the United States Department of Agriculture. a configuration that tends to favor pests over their Non-native insects must be held under strict quarantine natural enemies. Conservation

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